1. Field of the Invention
The invention relates generally to internal combustion engines and, more particularly, to two-stroke internal combustion engines. Still more particularly, the invention relates to exhaust gas discharge arrangements or systems for such engines, which exhaust gas discharge arrangements are intended to increase horse power output by applying a negative acoustical pressure wave or pulse at the exhaust port of the cylinder originating an outgoing pressure wave or pulse and by applying the positive outgoing acoustical pressure wave or pulse at the exhaust port of the immediately previously fired cylinder and at a time just prior to closure of the last mentioned exhaust port.
2. Reference to Prior Art
At least one exhaust gas discharge system has been known in the prior art for utilizing outgoing positive acoustical pressure waves or pulses occurring incident to the opening of an exhaust port subsequent to a cylinder firing to assist in evacuation of the burnt exhaust gas from the exhaust port and for increasing the density of the fuel/air mixture present in the cylinder which was immediately previously fired. More particularly, the prior exhaust gas discharge system operated to apply a negative acoustical pressure wave or pulse to an exhaust port of a cylinder originating an outgoing positive acoustical pressure wave or pulse, thereby diminishing the pressure at the originating exhaust port so as to assist in evacuation or scavenging of the burnt exhaust gas, and to apply the outgoing positive acoustical pressure wave or pulse to the exhaust port of the immediately previously fired cylinder at a time just prior to closure thereof so as to increase the density or quantity of the next charge in the immediately previously fired cylinder. Such application of a returning negative acoustical pressure wave or pulse so as to diminish the pressure at an open exhaust port is referred to hereinafter as "scavenging". Such application of a positive acoustical pressure wave or pulse prior to closure of an exhaust port is referred to herein as "plugging".
The prior exhaust gas discharge system is shown schematically in FIG. 1, is identified by the numeral 10 and is associated with an even firing V-block engine including first, second, third, and fourth cylinders 1,2,3,4, respectively, which are fired in the order 1-2-3-4, and which include respective exhaust ports 11, 12, 13, and 14 . Connected to the respective exhaust ports 11, 12, 13, and 14 are respective first, second, third and fourth cylinder exhaust gas discharge pipes or ducts 21, 22, 23, and 24 which are of equal length. The first and third cylinder exhaust gas discharge pipes 21 and 23 merge at a junction 26, and the second and fourth cylinder exhaust gas discharge pipes 22 and 24 merge at a junction 28. Extending from the junctions 26 and 28 are respective first and second exhaust pipes 30 and 32 which, in turn, merge at a junction 34. Also included in the prior exhaust gas discharge system or arrangement 10 is a third or exhaust gas discharge pipe 36 which extends from the junction 34 and, at its outer end, communicates with the atmosphere.
In operation, each acoustical pressure wave or pulse occurring consequent to each opening of the exhaust ports is generally identical.
More specifically, upon opening of one of the exhaust ports, i.e., for example, the second exhaust port 12, hereinafter referred to as the originating port, an outgoing acoustical positive pressure wave or pulse is discharged from the second cylinder 2 and travels through the cylinder exhaust gas discharge pipe 22 and through the exhaust pipe 32 to the junction 34.
From the junction 34, the outgoing positive acoustical pressure wave or pulse travels up the exhaust pipe 30 and up the cylinder exhaust gas discharge pipe 21 communicating with the immediately previously fired cylinder, i.e., to the exhaust port 11 of the cylinder 1, arriving there at a time just prior to closure of the exhaust port 11, thereby tending to push or plug fuel/air mixture in the cylinder exhaust gas discharge pipe 11 back into the cylinder and thereby plugging or increasing the density of the fuel/air charge in the cylinder 1.
At the same time, the outgoing positive acoustical wave or pulse also travels from the junction 34 outwardly through the exhaust discharge pipe 36 to the atmosphere. When the outgoing positive acoustical wave or pulse expands at the outer end of the exhaust discharge pipe 36, a negative acoustical returning acoustical wave or pulse is created, which returning negative wave or pulse travels back up the exhaust discharge pipe 36, past the junction 34, to the cylinder exhaust gas discharge pipe 22, and to the originating cylinder 2, arriving at the exhaust port 12 thereof at the time of scavenging thereof, i.e. at about the time when the associated piston is about at bottom dead center, thereby increasing the exhaust gas flow from the originating cylinder 2.
In the prior exhaust gas discharge system 10, the exhaust discharge pipe 36 had a length which was less then the lengths of the exhaust paths from the junction 34 to the exhaust ports 11, 12, 13, and 14. Furthermore, because of the relatively short length of the exhaust discharge pipe 36, the total time interval of outward and return acoustical wave travel in the exhaust discharge pipe 36 was less than the time interval during which the outgoing positive acoustical wave or pulse emanated from the originating exhaust port 12. As a consequence, the outgoing positive acoustical wave or pulse was still traveling through and past the junction 34 when the returning negative acoustical wave or pulse initially arrived back at the junction 34. As a consequence, the strength or magnitude of at least a part of the outgoing positive acoustical wave or pulse traveling toward the exhaust port 11 of the immediately previously fired cylinder 1 was diminished, with the result that less than an optimum increase in the fuel/air mixture density in the previously fired cylinder was obtained.
It is noted that, in the prior system, the blow down pulse, i.e., the exhaust gas pulse outgoing from the exhaust port, took place over a time interval such that the blow down pulse was still present at the junction 34 at the time when the returning negative wave arrived at the junction 34, whereby diminishment in the magnitude of the outgoing blow down pulse as well as of the returning wave occurred.
I other words, in the prior system shown in FIG. 1, the length from the junction 34 to the atmosphere was only about half of the length from the exhaust ports to the junction 34.
Attention is also directed to the following United States Patents:
______________________________________ 3,367,311 Tenney February 6, 1968 3,692,006 Miller, et al. September 19, 1972 4,116,172 Lohr, et al. September 26, 1978 4,732,118 Tanahashi, et al. March 22, 1988 4,732,124 Nakamura, et al. March 22, 1988 ______________________________________